Field of the Invention
The present invention relates to a sense circuit for use in a photoelectric conversion device or an image sensing device or the like for converting optical information such as light intensity or light wavelength or an optical image into electric current, electric charge or voltage, or electronic information containing digital data, and a method of operation of the sense circuit, and a photoelectric conversion array using the sense circuit.
Description of the Related Art
In the case of a photoelectric conversion cell in which an electronic information output is a voltage output, such as a CMOS (complementary metal oxide semiconductor) sensor, a voltage amplifier circuit has heretofore been used as a sense circuit. In this case, charging or discharging voltage on an output line connected to the output of the cell is high- and the connection of many cells to the output line leads to the connection of stray capacitances of high value in total to the output line and thus in turn a read speed is degraded, and further, very small voltage signals are buried in noise voltage which is superimposed on the output line, resulting in an impediment to enhancement of sensitivity.
Meanwhile, in cases where electronic information is obtained from a photoelectric conversion element which provides a current output, such as a photodiode, the sense circuit may possibly be devised to achieve high-speed operation; however, the same problems as above described are encountered in a sense circuit in which a resistance element is used to convert the current output into voltage.
Further, heretofore, it has been necessary for AD (analog-digital) conversion or the like that an output of the sense circuit be provided with a circuit to sample and hold a peak voltage or an average voltage, because, when output electronic information is subjected only to time-continuous processing which is continuous in time, an output voltage signal from the sense circuit varies greatly with time.
Meanwhile, techniques which involve integrating an output photocurrent from the photodiode and performing signal processing on an output voltage are disclosed in Japanese Patent Nos. 3146502 and 4286101. Problems inherent in the techniques are that an additional circuit to avoid switching noise is necessary because the output voltage is subjected to the signal processing while the photocurrent from the photodiode is passing through an integrating circuit, and that these techniques are unable to be used for processing signals from arrayed photoelectric conversion cells, because the photodiode is connected to the integrating circuit at all times. When a switching function for turning on or off an output current or the like is added to the photoelectric conversion element such as the photodiode in order to avoid the problems, switching control pulse noise is superimposed on the output, thus rendering it difficult to take out electronic information corresponding to feeble light.